1. Technical Field
The present technology relates to a method for manufacturing natural rubber, and particularly relates to a method for manufacturing natural rubber wherein viscosity can be lowered and processability can be enhanced by reducing a gel component in a natural rubber.
2. Related Art
Natural rubbers contain a high amount of a gel component compared to synthetic rubbers and, as a result, characteristically have a high rubber viscosity and various compounding agents are not easily dispersed uniformly therein. Therefore, when kneading a rubber composition that includes a natural rubber, the natural rubber must be masticated prior to kneading the various compounding agents in order to sufficiently break apart the rubber molecules, thereby lowering the rubber viscosity and increasing plasticity. However, problems exist in that conventional mastication requires a significant amount of energy and masticating leads to a decrease in the mechanical properties of the rubber. Furthermore, when time passes due to storing and transport of raw rubber as-is, the rubber viscosity increases due to an increase in the gel component. This leads to the problems of a reduction in the dispersibility of the compounding agents when kneading and a decline in processability.
To solve these problems, Japanese Unexamined Patent Application Publication No. 2005-23140A proposes lowering the viscosity of a natural rubber and suppressing an increase in rubber viscosity over time by mixing a viscosity stabilizer in a natural rubber latex, and then solidifying and drying this mixture.
Additionally, WO2007/049460 proposes a process for producing a solid natural rubber wherein a metal content in a natural rubber latex is reduced by treating the natural rubber latex with a water soluble ammonium salt, and then dried by spraying the product into a pulse wave atmosphere.
However, the method for manufacturing natural rubber described in Japanese Unexamined Patent Application Publication No. 2005-23140A has a problem in that the conventional viscosity stabilizers hydroxylamine, hydroxylamine sulfate, and hydroxylamine hydrochloride are not readily usable from a health and safety perspective due to high levels of danger and toxicity.
Additionally, the natural rubber obtained via the manufacturing method described in WO2007/049460 has a problem in that while rubber viscosity immediately following production can be reduced, the gel component increases with the passage of time, and this leads to the rubber viscosity increasing again. Compounding a viscosity stabilizer in order to suppress an increase in rubber viscosity over time is commonly known, however, viscosity stabilizers such as hydroxylamine, hydroxylamine sulfate, and hydroxylamine hydrochloride are not readily usable from a health and safety perspective due to high levels of danger and toxicity.
Therefore, there is a demand for a method in which these hydroxylamines are not used and there are no health and safety problems whereby the viscosity of a natural rubber is lowered and processability is enhanced by reducing the gel component of the natural rubber.